1. Field of the Invention
The present invention is directed to a wavelength compensated optical wavelength division coupler, more particularly to an integrated coupler.
2. Description of Related Art
Optical multipexers/demultiplexers are generally known in the art. See, for example, U.S. Pat. No. 4,244,045 entitled xe2x80x9cOptical Multiplexer and Demultiplexerxe2x80x9d, which is hereby incorporated by reference in its entirety for all purposes. In the configurations set forth therein, the mux/demux includes a plurality of filters for the respective wavelengths, a corresponding plurality of prisms for providing the filtered light from/to a corresponding plurality of sources/detectors and a corresponding plurality of elements for collimating/condensing light. The multiplex path that either receives or supplies the multiplexed light includes a prism and an element for condensing/collimating light.
As can be seen in the ""045 patent, a plurality of narrow band pass filters are required, one for each of the channels. To multiplex a plurality of channels requires a plurality of narrow band-pass (NBP) filters connected in series such that the output of one filter provides part of the input to another. This serial connection typically requires a critical off-axis alignment that must be precisely controlled. As shown in the ""045 patent, this involves introducing a light beam at a desired incident angle using the lens and the prism. Since each of the multiple beams required a different incident angle, different prisms are used for each beam. These prisms are very small, making them difficult to manufacture and making further reduction in size of the multiplexer impractical. Another example of such adjustment includes fixing the NBP filters and then adjusting the location of the ports for the input and output of light to thereby control the angle of incidence on the filter. Since each beam requires different angles, and thus different prisms, in using these configurations for multiple beams, very small different prisms are required.
Attention has been focused on eliminating these small parts and separate filters. One solution involves using linear variable filters, as set forth in U.S. Pat. No. 5,583,683 entitled xe2x80x9cOptical Multiplexing Devicexe2x80x9d to Scobey. The device disclosed therein is a parallel optical block having a filter of varying thickness on at least one side thereof. The light is incident on the block at the same tilt angle, but due to the varying thickness of the filter, different wavelengths are transmitted at each port, with the remaining wavelengths being reflected, again creating the zigzag pattern of the ""045 patent. However, thickness control is difficult to reliably achieve and the control of the input tilt angle is also critical. Another solution involves using a wedge-shaped optical block with the filter on at least one side thereof. The wedged shaped optical block used therein results in the sequentially reflected light beams striking the wavelength selective filter at different angles.
However, even these integral filter element solutions still require precise control of either filter thickness or wedge profile. Further, the number of channels to be practically multiplexed by the variable filter thickness is limited by process control and to be practically multiplexed by the wedge shaped due to the increased length needed to accommodate many channels. Therefore, while these configurations may overcome some of the attendant problems of numerous separate filters, they still require expensive angular alignments.
The present invention is therefore directed to an integrated coupler that substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art.
It is an object of the present invention to create a multiplexer having fewer individual parts, thereby improving manufacturability and scalability.
At least one of these and other objects may be realized by providing an optical device including a wavelength selective filter, a first port for propagating at least a first wavelength, a second port for propagating at least a second wavelength different from the first wavelength, a third port for propagating at least the first wavelength and the second wavelength, and at least two individual optical elements, each optical element being associated with one of the ports, between an associated port and the wavelength selective filter, wherein all optical elements needed for directing light between the ports and the wavelength selective filter are provided on at least one of a substrate and substrates bonded thereto. All three ports are positioned relative to the wavelength selective filter.
The wavelength selective filter and the at least two optical elements may be integrated on a wafer level. The wavelength selective filter may be a multi-layer dielectric stack formed on one of the substrates. The bonding of substrates may occur at a wafer level, and the bonded substrates are diced to form the optical device. The at least two optical elements may be formed lithographically.
The at least two optical elements may be diffractive elements. The diffractive elements may have a same deflection grating. The at least two diffractive elements may include at least three diffractive elements. The diffractive elements may perform both deflection and collimation. The at least two optical elements may be refractive elements. The refractive elements may be off-axis refractive elements. The at least two optical elements may include a pair of optical elements. The pair of optical elements may include a refractive element and a diffractive element. All optical elements may be provided on a single substrate. The at least two optical elements may be provided on a same surface.
The optical device may include light sources adjacent to substrates on which optical elements are formed. The optical device may include power monitors for the light sources. The at least two optical elements may deflect a portion of the light from each of the light sources onto a respective power monitor.
At least one of the above and other objects may be realized by providing a diffractive multiple wavelength optical coupler including at least two diffractive elements having a same deflection grating period, each diffractive receiving a substantially monochromatic light beam, a wavelength selective filter for at least one of the at least two diffractive elements, the wavelength selective filter passing a desired wavelength and reflecting all other wavelengths; and a multiplex diffractive receiving a multiplex optical signal. The coupler may serve as a multiplexer or a demultiplexer. The at least two diffractives may include at least three diffractives, wherein a spacing between adjacent diffractives is different from one another.
At least one of the above and other objects of the present invention may be realized by providing a multiple wavelength optical coupler including at least a first, second and third surface on which an optical function is performed, at least two individual optical elements, each individual optical element receiving a substantially monochromatic light beam, the at least two individual optical elements being formed on the first surface, a wavelength selective filter that passes a desired wavelength and reflect all other wavelengths formed on a second surface, the third surface reflecting light incident thereon, and a multiplex optical element receiving a multiplex optical signal.
The coupler may serve as a multiplexer or as a demultiplexer. The individual optical elements may be refractive elements and/or diffractive elements. The at least two individual optical elements may include at least three individual optical elements, wherein a spacing between adjacent individual optical elements is different from one another.
At least one of the above and other objects may be realized by providing a multiple wavelength optical coupler including at least three separate optical elements, each individual optical element receiving a substantially monochromatic light beam, wherein each separate optical element outputs light at a different deflection angle and a spacing between adjacent individual optical elements is different from one another, a plurality of wavelength selective filters, a wavelength filter being provided for at least two of the three separate optical elements, each wavelength selective filter passing a desired wavelength and reflecting all other wavelengths, and a multiplex optical element receiving a multiplex optical signal. The coupler may serve as a multiplexer or as a demultiplexer. The separate optical elements may be refractive elements and/or diffractive elements.
At least one of the above and other objects may be realized by providing a method of coupling multiple wavelengths including receiving a plurality of substantially monochromatic light beams at a corresponding plurality of ports, each port receiving a monochromatic light beam of a different wavelength, providing an optical element at each port, each optical elements outputting light at a particular deflection angle, wavelength selectively filtering at each non-terminal port, the filtering including passing the substantially monochromatic light beam associated with the port and substantially reflecting all other wavelengths, directing the substantially monochromatic light beams between the optical elements and a multiplex port, and receiving a multiplex optical signal at a multiplex port. The providing may include, when there are at least three optical elements, spacing adjacent optical elements differently from one another. The optical elements may output light at the same or different, unique deflection angles.
These and other objects of the present invention will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.